Traveling wave electron interaction device having efficiency enhancement means

ABSTRACT

Phase-focusing means are introduced into a traveling wave electron interaction device to optimize exchange of electron kinetic energy with electromagnetic waves propagated along an adjacent wave-guiding structure by providing an intermediate phase velocity profile at a relatively low level of electron beam energy extraction and well before tube saturation. The resultant redistribution of the guided wave phase velocity provides a delay in the electromagnetic circuit sufficient to permit advancement and desynchronizing of electron bunches to a position in the decelerating field of the propagated waves where the forces on the electrons are substantially minimal. Retention of electrons for longer periods in the decelerating field region of the circuit waves has resulted in a highly significant enhancement in efficiency in traveling wave tube performance. Application of similar phase velocity shift techniques has substantially reduced harmonic frequency power content leading to premature tube saturation in high-gain octave bandwidth devices to yield improvements in efficiency by approximately a factor of 2.

United States Patent [72] Inventor Norman J. Dionne Ithaca, N.Y. [21]Appl. No. 33,459 [22] Filed Apr. 30, 1970 [45] Patented 'Oct. 19, 1971[73] Assignee Raytheon Company Lexington, Mass.

[54] TRAVELING WAVE ELECTRON INTERACTION DEVICE HAVING EFFICIENCYENHANCEMENT MEANS 8 Claims, 12 Drawing Figs.

INPUT INPUT VELOCITY SECTION SHIFT SECTION No.1

Primary ExaminerI-Ierman Karl Saalbach Assistant Examiner-SaxfieldChatmon, Jr.

Attorneys-Harold A. Murphy, Joseph D. Pannone and Edgar 0. RestABSTRACT: Phase-focusing means are introduced into a traveling waveelectron interaction device to optimize exchange of electron kineticenergy with electromagnetic waves propagated along an adjacentwave-guiding structure by providing an intermediate phase velocityprofile at a relatively low level of electron beam energy extraction andwell before tube saturation. The resultant redistribution of the giiidedwave phase velocity provides a delay in the electromagnetic circuitsufficient to permit advancement and desynchronizing of electron bunchesto a position in the decelerating field of the propagated waves wherethe forces on the electrons are substantially minimal. Retention ofelectrons for longer periods in the decelerating field region of thecircuit waves has resulted in a highly significant enhancement inefficiency in traveling wave tube performance. Application of similarphase velocity shift techniques has substantially reduced harmonicfrequency power content leading to premature tube saturation inhigh-gain octave bandwidth devices to yield improvements in efficiencyby approximately a factor of 2.

OUTPUT VELOCITY v SHIFT SECTION No.2

WAVE PHASE VELOCITY RATIO (v /c) sum 3 or e PATENTEDucI 19 Ian 6 6 INPUTA BEAM VELOCITY OUTPUT PHASE VELOCITY 7HIFT //4 A I -|.o 3 I U /28 Q 5.2 I30 I -06 I /26 'o.4 E; /20 m SECTION A SECTION B o- I l r I i I- I:20 40 so I00 A :20 I40 Z-LENGTH ALONG CIRCUIT (BAR N0.)

:- INVEN TOR BY Z ATT ORNE Y TRAVELING WAVE ELECTRON INTERACTION DEVICEHAVING EFFICIENCY ENHANCEMENT MEANS BACKGROUND OF THE INVENTION 1. Fieldof the lnvention The invention relates to traveling wave electroninteraction devices for amplification or generation of high-frequencyelectromagnetic wave signal energy.

2. Description of the Prior Art 0.63

Traveling wave devices commonly incorporate a wave-guiding structure ofa predetermined periodicity such as, for example, a helix forpropagating high-frequency (RF) electromagnetic energy to be amplifiedby extracting kinetic energy from a high-power beam of electrons. Thewave energy travels along the structure at a velocity less than thevelocity of light. The electric and magnetic'fields of such energyinduce perturbations in the beam in the fonn of electron packets orbunches having a fundamental frequency component at substantially thefrequency of the energy on the wave-guiding structure. Numerous harmonicfrequency components may also be present in the perturbed electron beam.Conventionally, in such devices the electron beam is translated alongthe length of the guiding structure which retards the velocity ofelectromagnetic circuit waves until a synchronous relationship isestablished to optimize exchange of energy between the beam and waves.

Electron bunches which traverse the interaction path at a group velocityconsidered to be in step with the retarded electromagnetic fields thenmove at substantially the phase velocity of the wave-guiding structure.The electron beam, therefore, becomes simultaneously velocity anddensity modulated along its path of travel until a saturation point isreached where the kinetic energy extracting is maximum and the beampackets become disarranged. The electron beam modulation is a result ofthe phenomenon known in the art as phase focusing" and intensifiesprogressively along the beam path towards the 'output end of the devicewhere a collector electrode is positioned.

The high-frequency RF energy devices under consideration, therefore,provide for the continuous and prolonged interaction between electronsand electromagnetic fields on the guiding structure. Such devices aregenerically referred to in the art as traveling wave electroninteraction tubes and may be characterizedas of the backward or forwardwave type. In a backward wave device the electron beam travels at avelocity which is synchronous with the phase velocity of a travelingwave space harmonic component moving in a direction opposite to that ofthe energy flowing along the wave-guiding structure. The electron beam,therefore, travels in one direction and the energy of the induced wavetravels-in the opposite direction. In forward wave devices the electronbeam and energy of the induced wave characteristically travel in thesame direction. The wave-guiding structure in the backwardwave-typedevice is constructed so that the phase velocity of the fundamentalfrequency determining component travels in a direction inverse to thedirection of the electron group velocity. In contradistinction, aforward wave device is provided with a wave-guiding structure soconstructed that the phase velocity of the fundamental frequencycomponent is in the same direction as the electron group velocity. Theexpression fundamental" utilized in the description of the invention isdefined as that component of an electromagnetic wave having the largestphase velocity.

The high-frequency electric fields of the propagated waves havetransverse and axial components. The axial component accelerates anddecelerates the velocity of the electrons and brings them into afavorable phase focused position to thereby give up their energy to theelectric field of the wave and enhance its amplitude. To an electronmoving in a reference plane with the same velocity as the phase velocityof the wave the high-frequency axial field appears stationary. The axialcomponent of the field, therefore, is primarily involved in the inducedbeam modulation. It has been noted in the art that with more electronsin the decelerating or retarding field of the high-frequency electricfields of the propagated waves a net increase in transfer of energyoccurs. In traveling wave tubes a significant performance parameter tobe considered is efficiency which is a measure of the energy convertedfrom kinetic energy on the beam to the RF energy in the wave travelingadjacent to the beam. This parameter is an arithmetic ratio of the RFenergy output power to the input power and generally values of 20percent and under have had to be accepted. In existing systemswithrather high voltage supplies already required for biasing thewave-guiding structure relative to the electron beam source any increasein efficiency must desirably be made utilizing present tube structuresand existing power supplies.

Several methods have been heretofore advanced in the art to increasetube efficiency characteristics. Observers have, however, suggested theapplication of such enhancement techniques only in the region of thebeam path where the electron bunches slow down and electrons slip intothe ac celerated region. These faster moving electrons are considered tobe out of phase and actually extract energy from the high-frequencywaves on the wave-guiding structure. One prior art technique involvesreducing the phase velocity of the waves by changing the pitch of theguiding structure com ponents in the appropriate manner to vary thephase velocity. Such devices, therefore, would require the pitch of, forexam ple, a helix-type structure to be altered to slow the phasevelocity down progressively near the output end of the device. US Pat.No. 2,846,6l2, issued Aug. 5, I958 to T. E. Everhart exemplifies thistechnique. Still another technique involves the application of separatevoltage potential jumps to the guiding structure particularly atintermittent points where the electrons in the beam have slowed down.The technique requires the addition of numerous voltage supplies atincreased expense together with accompanying disadvantages. An illustration of the voltage jump technique may be found in US. Pat. No.2,817,037, issued Dec. I7, 1957 to R. W. Peter.

The foregoing techniques while improving efficiency performance intraveling wave electron interaction devices, do not prepare orprecondition the beam modulation at low levels of energy extraction forthe purpose of optimum effciency enhancement. Further, in such devicesutilized for octave bandwidth applications the presence of interferringharmonic frequencypower at the low or fundamental frequency end of theband has led to very low efficiency in performance due to premature tubesaturation.

An application for the employment of the devices under considerationwould be phased array radar systems wherein the antenna remainsstationary while the radar beam is transmitted in a scan patternelectronically at very fast rates of speed. Traveling wave tubeamplifier chains feed a plurality of the antenna elements to radiatemany millions of watts of energy over a scanning wave front. Ratherlarge on-site voltage sources are required when one considers, forexample, that to achieve an output RF signal of l watt approximately 20watts of beam power is required in tubes having only a 20-percentefficiency. Enhancement of efficiency, therefore, will provide forhigher power output radar signals to increase scanning distances withoutaltering overall tube dimensions or on-site power facilities. In someinstances tube sizes may even be reduced as a result of the50-60-percent efficiencies envisaged in the practice of the presentinvention at specific frequency ranges.

SUMMARY OF THE INVENTION In accordance with the present invention aunique result has been achieved in increasing efficiency in travelingwave devices by preconditioning electron beam modulation through novelphase-focusing means. The phase velocity of propagated waves on theelectromagnetic wave-guiding circuit adjacent to the beam may be alteredin such a manner as to deliberately shift the phase of the modulatedelectron bunches and introduce a desynchronization effect at low levelsof beam modulation. The criteria to be considered involves shifting ofthe electron bunches further forward in the decelerating field of thesinusoidal electromagnetic electric fields thereby providing for longerperiods of extraction of beam energy before tube saturation. The overallprofiling of the phase velocity characteristics of the electromagneticwaves to produce a desired result is based on a computerized output of amathematically simulated model having programmed inputs of electron andtube structural characteristics. The computer program is based on anormalized nonlinear large signal analysis disclosed in the an by suchauthorities as J. E. Rowe, P. K. Tien, H. C. Poulter, M. E. El-Shandwilyand A. J. Giarola in references to be hereinafter renumerated. Anintermediate velocity is produced by a circuit phase shift atsubstantially low levels of beam modulation where the interactionbetween electrons and waves is substantially minimal and power levelsare in the order of, for example, 1-1 percent of the DC beam power. Themotion induced in the modulated beam bunches primarily advances the beamvelocity relative to the wave toward the forward portion of thedecelerating field.

The practice of the invention is not restricted to any particularwave-guiding circuit structure and efficiency enhancement will berealized in devices employing helices, as well as interdigital delaylines, ring and bar lines and any other periodically loaded structures.The position of the beam conditioning to shift electron velocity in apredetermined manner is accurately located relative to the predictedbunching phenomena for any particular tube construction. The waveguiding structure also can be varied in many different ways selected bythe tube engineer. Such modification techniques may comprise severs,negative and positive tapers, closerspaced periodic structures, voltagejump, lumped phase shifters or any other well-known methods, eitherindividually or in combination. The important characteristic to bear inmind is that the intermediate velocity to introduce the element ofdesynchronization occurs at low levels of beam modulation and energyextraction considerably before tube saturation. The duration desired forthe desynchronization effect before restoration of the synchronous beamand wave relationship is also subject to analysis in accordance with theprogrammed output of the computer study.

In an exemplary embodiment of a traveling wave device for high-gainrelatively broadband high-frequency applications the efficiency factorwas increased from 20 to 41 percent. An octave bandwidth embodiment hasalso evolved with virtually hannonic free performance and efficiencydoubled from 15 to 30 percent. Tube efficiencies of 50 to 60 percent andreduced size will now be realizable through the utilization of theinvention as well as depressed collector operation, which permits evenfurther efficiency gains. Further, the additional measure of stabilityafforded by the velocity shift technique reduces backward waveoscillations.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the detailsfor the provision of preferred embodiments will be readily understoodafter consideration of the following detailed description and referenceto the accompanying drawing wherein:

FIG. 1 is a schematic representation of a prior art traveling wavedevice of the forward wave-helix type;

FIG. 2 is a plot of the programmed response of phase and velocity of anelectron beam in a simulated device without velocity shift profiling;

FIG. 3 is a plot of the programmed response of phase and velocity of anelectron beam in a simulated device having a wave phase velocity shift;

FIG. 4 is a schematic representation of a method of implementing theinvention in a helix-type traveling wave device;

FIG. 5 is a diagram of the profile of the wave phase velocity ratioalong the axial length of the device;

FIG. 6 is a diagrammatic representation of an alternative embodiment ofthe invention incorporating tapers, as well as a velocity shift in thepropagated wave profile;

FIG. 7 is a perspective view of a ring and bar delay line structureembodying the wave phase velocity profile shown in FIG. 6;

FIG. 8 is a graph of the normalized force versus phase for fundamentaland harmonic waves near tube saturation;

FIG. 9 is a graph of the relative phase of beam charge density versusnumber of beam wavelengths;

FIG. 10 is a graph of the power conversion efficiency relative to theforce field along the tube length of illustrative devices with andwithout the velocity shift;

FIG. 11 is a graph illustrating power gain as a function of distance inbeam wavelengths for devices with and without the velocity shift;

and FIG. 12 is a schematic representation of a device having a separatecoupled phase shifter.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,FIG. I, particularly a waveguiding structure 2 is illustrated extendingaxially within an envelope 4. The wave-guiding structure has beenillustrated as a unifilar helix having an equal number of spaced turns,however, as previously noted any other guiding structure may beemployed. Microwave energy to be amplified is coupled to one of therespective ends of the helix by input means 6 and output coupling means8 disposed at the opposing end of the device. An electron beam emittersource 10 is disposed at the end of the tube envelope adjacent the inputmeans 6 and includes means for guiding the stream of electrons l2axially through the helix 2. Adjacent the output end of the envelope acollector electrode 14 is shown to provide for collection of the spentelectron beam.

The electron emitter 10 comprises an emissive cathode l6 and heater coil18 together with suitable leads extending through the envelope forconnection to appropriate DC voltage biasing sources. A beam-focusingmember 20 is provided in the intennediate region between the input endof the helix and the cathode emitter. This member is biased positively asufficient voltage to accelerate the electrons along the desiredtrajectory path. A grid control electrode 22 is positioned adjacent tothe cathode emitter and is biased by a DC variable supply 24.Magnetic-field-producing means 26 surround the overall tube envelope toassist in providing a longitudinal magnetic field parallel to the pathof the electron stream. The illustrated device is referred to in the artas of the 0" and forward wave type for amplification of electromagneticenergy.

Before proceeding to a detailed disclosure of embodiments of theinvention the large signal analysis using digital computer techniques todetermine simulator tube characteristics will be examined. The nonlinearmultisignal large signal analysis has been employed to study bothfundamental and harmonic frequency generation as it is related totraveling wave devices having relatively nondispersive wave-guidingstructures. As is well known in the art the term dispersive refers tothe ratio of phase velocity of the traveling waves and the groupvelocity of the traveling wave and a nondispersive structure would beone in which the ratio is substantially equal to unity over thefrequency range utilized.

Basically, the programmed mathematical model is a direct specializationof the large signal analysis of .l. E. Rowe, Transactions, ProfessionalGroup of Electron Devices IRE, Vol. ED3, pps. 39-57, Jan. 1956 and is astraightforward extension of the one-dimensional analysis of H. C.Poulter, Technical Report No. 73,0NR Contract NGonr 251(07), ElectronicsResearch Laboratory, Standford University, Jan. 1954, as well as P. K.Tien, Bell System Technical Journal, Vol. 35, pps. 349-374, March 1956.

The employed analysis is based on the following assumptions:.

l. The interaction between the RF electromagnetic wave and the electronbeam occurs in only one space harmonic component of the total circuitfield at each frequency.

. The RF electric field is uniform across the beam, which is constrainedto have no radial velocity component.

. The phase velocities of the beam and circuit wave are much less thanlight. Therefore, nonrelativistic mechanics can be employed and Poissonsequation can be used in place of the wave equation for the determinationof the space charge fields.

4. RF magnetic fields can be neglected.

Using a continuous transmission line to represent the traveling wavecircuit for the desired space harmonic, it has been shown by theaforereferenced Poulter, Rowe, as well as M. E. El-Shandwily, Universityof Michigan Technical Report No. 85, Electron Physics Laboratory, AnnArbor, Mich., June 1965, that circuit voltage can be related to thebeam' charge density at the n"angular frequency (ru by:

Where 0,, and d, are the well-known J. R. Pierce gain and lossparameters respectively denoted in his text Traveling Wave Tubes, D.VanNostrand Co., New York 1950. The beam coupling impedance Z, is thatfor the appropriate unloaded circuit wave space harmonic having a phasevelocity v,,.

According to custom, we define two normalizations distance and wavevoltage amplitude. The normalized distance is given by:

where u is unloaded beam velocity and z is the axial position along thecircuit. The circuit wave voltage amplitude is normalized by:

where l =DC beam current.

In these normalizations, the phase of the n'" harmonic is related to theindividual charge group phase by the equation:

where 0,,(z) is the phase lag of the circuit wave at z relative to amoving reference frame having the initial beam velocity, u,,.

Application of the continuity equation and a Fourier expansion of thebeam charge density together with the previously stated relations resultin the desired large-signal circuit equations which now follow: I

The appropriate phase equation can then be written as:

Mimi 2m (7) Finally, the force relation can be expressed as:

In this equation F (D-4 is the space charge weighting function asdefined by Poulter.

Equations 5, 7 and 8, therefore, comprise a complete set ofdifferential-integral relations which can be solved in finite differenceform on a high-speed digital computer.

To derive the simulated analysis of the traveling wave tubeefficiencies, the frequency characteristic of both the phase velocityand the axial-beam-coupling impedance of the fundamental space harmonicassociated with the wave-guiding structure are of primary consideration.Usually, during the computer operation the trajectories of 32 electroncharge groups, which are initially equally spaced over one period in thetime-phase domain, are followed incrementally along the length of thesimulated tube. The input power of each space hannonic is related to thestarting normalized circuit wave amplitude by the expression:

More generally, the power along the wave-guiding circuit may beexpressed by:

215 ,01 n d e n(1+C,,b,,) c1

and the basic electronic conversion efficiency at the fundamentalfrequency is calculated from the following equation:

Referring next to FIGS. 2 and 3 the results of the computerized analysisis plotted showing the electron velocity and phase (both normalized) ona time-phase domain basis spaced over one period at various positionsalong the interaction path of the simulated tube modeLEach dotdesignates the modu:

lated trajectory of one of the approximate 32 electron charge groupsanalyzed. The dashed lines 30 and 32 in FIGS. 2 and 3, respectivelyrepresent an equipotential surface along which the electrons areintroduced at an average velocity normalized to a value of 1.0.The phaseof the electron groups having a designated numerical value of between-0.5 and 40.5 is plotted along the horizontal coordinates and representsthe normalized condition of the conventional -1rand +1rphaserelationship with respect to the number of beam wavelengths along theinteraction path. The computed velocity values are plotted along thevertical coordinate and cover a range of values form 0.3 to 1.4. FIG. 2illustrates the electron group characteristics in the simulatedtraveling wave tube of prior art construction. Fig 3. refers to the samecharacteristics of an illustrative embodiment of the invention havingthe profiled velocity shift phase-focusing means to increase efficiency.

The first reference frame in FIG. 2 depicts the initial beam modulationnear the beginning of the interaction path where the level of suchmodulation is extremely low. The series of electron group trajectoriestraversing the periodic interval in the time-phase domain arecollectively referred to by the numeral 34. A substantially sinusoidalpath is noted with the decelerating field region oriented below line 30while the accelerating or higher velocity electrons are bunched abovethe reference line. In accordance with well-known procedure the initialelectron beam velocity is adjusted to be slightly greater than thevelocity of the electromagnetic waves traveling in the same direction tooptimize synchronous interaction. Consequently, the electronphase-focusing path assumes a deviation slightly to the right of theOvalue crossover point in the reference frame.

Referring to the next position down the line we note the commencement ofthe formation of compact bunches in the decelerating field region,particularly at point 36 by reason of the modulating forces exerted onthe electrons by the highelectric fields of the adjacent propagatedwaves. It will be noted that the prior art bunching to achieve a netinteraction of electron kinetic energy with the guiding circuit wavescommences at a normalized phase value of approximately 02.-0.3 or nearthe point of maximum decelerating forces in this field. The electronshave begun to slow down sufficiently to achieve the net transfer ofenergy and increase the amplitude of the axial electric field of theelectromagnetic waves.

Still farther down the interaction path the electron groups will beobserved to have even a tighter more definitive compact bunching patternindicated by numeral 38. As the bunching becomes more compact theelectromagnetic waveform illustrated by curve 40 continues to increasein amplitude by the appreciable fraction of kinetic energy convertedinto energy stored in the wave. The electromagnetic wave propagating onthe guiding circuit has been shown only in this reference frame sincethe invention is dealing principally with the reorientation of theelectron-bunching phenomena by preconditioning the beam for the regionwherein the synchronous interaction bunching is established. Theelectromagnetic wave has been plotted with the horizontal line 42indicating circuit modes along the interaction path and the arrow 44indicates the amplitude of the electric field forces on the electrongroups. The maximum bunching then, occurs in the approximate regionshown by line 46 indicating the point of maximum decelerating force onthe moving electron groups.

In the subsequent frame we observe saturation commencing when the totalnumber of electrons in the accelerating and decelerating fields becomesubstantially equal. The disarray of the previous tight bunches is notedin the area indicated by bracket 48. Further, electron groups 48, 50, 52and 54 have drifted back into the accelerating region and are now ofvery little consequence for any further amplification.

In the final frame full saturation condition is achieved. Since thehigher velocity electron groups rob energy from the propagated waves anundesirable condition is revealed in that the electron groups above thedashed line 30 indicated by the bracket 58 have relatively highvelocities in the range of from 01. to 1.2. These electrons, therefore,have contributed relatively little to the net interaction process. Suchresidual fast" electron groups at full saturation, then, indicate apossible area of efficiency enhancement by more complete utilization ofthe energy in electrons nearer the input region. The observationofelectron groups having high-residual energy has continually plaguedtraveling wave interaction tubes since the high heat generated uponcollection limits the power capabilities.

Bearing in mind then the observed inefficient phase focusing of electrongroups in the simulated mathematical tube models of prior art devices, adevice incorporating a suggested structure for enhancing efficiency bymore favorable phase focusing will now be described. Attention isdirected to FIG. 3 and in connection with this discussion theelectromagnetic field waveform diagram shown in the middle referenceframe has been numbered similarly to the one shown in FIG. 2.

Initial modulation shown by the collective path 60 is substantiallysimilar in this region to the prior art devices. It is shortlythereafter, however, that the concept of the invention attempts tointroduce a velocity shift at relatively low levels of beam energyextraction in order that a deliberate desynchronization will take placewith the electron groups going faster than the propagated wave electricfields. At a subsequent position down the interaction path thesynchronous relationship is restored. The primary objective of theinvention resides in the shifting of the slower moving electron groupsto a new position within the decelerating field region where they willbe able to give up energy to the circuit waves over considerably longerperiods of time. The shifting of the electron groups is desirably in aforward manner within the decelerating field toward the tube output end.This also permits a larger fraction of the electron groups to beeventually exposed to the decelerating field toward the tube output end.This also permits a larger fraction of the electron groups to beeventually exposed to the decelerating field before reaching tubesaturation. The new velocity shift region is referred to in thespecification as one of minimal decelerating forces and is locatedsubstantially between the -and 0 electromagnetic wave velocity value.

In the next frame the effects of the incorporation'of structure forproviding the phase-electron beam velocity shift will be noted. As aresult of the desynchronization of interaction, the tight compactbunching previously noted in FIG. 2 at point 36 has now been movedslightly to the right to point 62 at phase value of between 0.4-0.5.Further on down the interaction path we observe a trajectory indicatedgenerally by the numeral 64 with the slower moving electrons now beingshifted to a point 66 within the decelerating field region. In relationto the electromagnetic waveform 40 the tight bunching of electron groupsis now in the forward portion of the decelerating field as indicated bythe line 68 in the region of between 90 and 0 wave phase velocity.

The level of beam modulation where the desired shift is provided tospeed up the electron bunches or retard the propagated waves willgenerally be found in the region of from 20-10 db. down from the tubesaturation or in the region of approximately l-percent efficiency. Theregion will vary from device to device depending on operating frequencyand bandwidth characteristics to provide an advance and/or retardationgenerally in a range of from 3590. The manner of achieving the shift inphase focusing can be achieved in many ways depending on the waveguiding and beam parameters employed. Generally, such techniques asdelay line severs, delay line tapers of the positive and/or negativevariety, beam voltage potential jumps, separate phase shifters coupledto the waveguiding circuit individually or combined can be employed. Theanalysis and judgment of the engineer is decisive to now provide adevice having a programmed response determined mathematically withoutthe need for costly empirical verification through construction of manyprototype models. The intermediate velocity shift is provided eithersingularly along the interaction path or dually when a reestablishmentof the beam-wave synchronization is desired at a particular level ofcircuit phase velocity ratio (VpC). In the illustrative embodiment ashift of approximately 45 was introduced in the phase velocitypropagating characteristics.

The subsequent reference frame illustrates an electron group path 70having resynchronization established by a second velocity shift means,still well before the large signal region. The tight compact bunching atpoint 72 will be observed to be in the 0.3-0.5 phase value.

The beginning of the saturation reference frame has been purposelyomitted to illustrate the resynchronization effect and would besubstantially similar to the view in FIG. 2 which illustrates thebeginning of the breaking up of the uniform electron bunch distributionand movement of electrons towards the accelerating field after giving uptheir energy. Turning next to the final view of complete saturation,however, the full import of the invention will be noted. The groupsmoving toward the accelerating field are indicated by the bracket 74while those still in the decelerating field are indicated by the bracket76. First, it should be observed that there are a larger number ofelectron groups approaching the accelerating field which indicates thatthey have delivered their kinetic energy to the circuit waves. In theanalogous situation for prior art devices in FIG. 2 there are moreelectrons in the decelerating field awaiting a chance to exchange energybut never accomplishing this result because of saturation.

Secondly, whereas in the prior art situation we note a large number offast" electron groups above the electron velocity value of 1.0 withinthe bracket 58, now in the embodiment of the invention there is only onegroup of high-velocity electrons 78. This indicates more electrons havenow been shifted to a more favorable phase-focusing position in thedecelerating region for the net transfer of energy.

Further it should be noted that by the time the electron groups in thenew embodiment reach tube saturation and drift back towards theaccelerating field, the velocity values are considerably below thelevels of the prior art embodiments. If the number of electron groupssay at the 0.7 level of velocity and above at full saturation in FIG. 2were counted, there would be nine such groups. These higher velocityelectron groups indicate an inefficient net exchange of energy with thewaves. In the exemplary embodiment of the invention in FIG. 3, however,only five such electron groups are noted above the 0.7 level and sixelectron groups are found in the 0.4 to 0.7 level. In addition, thereare a total of seven groups ofelectrons which have given their energy tothe waves and moved over to the accelerating region in the 0.4 to 0.7level whereas in the prior art there were only three groups. Thevelocity shift to the forward portion of the decelerating region hasactually been able to provide an additional amount of kinetic energy bya factor of from one-fourth to one-third to thereby increase poweroutput by an efficiency factor of from25-33l/3 percent. With otherimprovements in tube structural characteristics such as depressedcollector operation, overall efficiency improvement factors of40-60percent are now permissible.

Referring next to FIGS. 4 and 5 a helix-type delay line incorporatingthe teachings of the invention will be described. In FIG. 4 a helix-typewave-guiding structure 80 is illustrated incorporating the features ofthe invention for use in a forward wave-traveling wave interactiondevice similar to that shown in FIG. 1. In FIG. 5 a profile of the wavephase velocity ratio (Vp/C) where c is the speed of light is plottedover the length of the interaction path and indicated generally by line82. The DC electron beam velocity which, as heretofore stated, isslightly greater than the propagated waves is plotted as dashed line 84.The input secton 86 of the helix has a predetennined substantiallyuniform pitch, a term defined as the reciprocal of the number of turnsper unit length. The characteristics of the wave-guiding structure inthis region will follow conventional techniques for initial beammodulation and provides for a substantially constant phase velocityratio adjacent the input end as shown by line portion 88 of the profilediagram.

At the point still at relatively low depths of beam modulationdetermined by the skilled artisan from analysis and the computerizedstudy, a phase velocity shift in distances typically less than thefundamental circuit wavelength is in troduced by means ofa change inhelix pitch or circuit-loading member of the wave-propagating structure.The characteristic slope of the profile at this juncture can berepresented by line portion 92. The phase velocity drops to a new levelto substantially desynchronize the interaction process and allow thebeam bunches to move or slide ahead faster in relation to the propagatedwaves. This shift creates an intermediate velocity region 94 in theprofile diagram and since a tighter or closer spaced helix reduces phasevelocity, an intermediate helix section 96 is provided to accomplish thedesired result.

Resynchronization is established at a point 98 along helix 80 alsopredetennined by the computer analysis. Another velocity shift will,therefore, be introduced and a phase velocity 100 will be established intraversing the large signal region 106 before collection at the outputend of the tube. Line 102 indicates the step to the new phase or outputvelocity on the profile diagram. The dual velocity shift concept,therefore, provides in essence what may be described as a notch over apredetermined interval in the tube phase velocity characteristics toachieve the desired reorientation of the electron bunches. The new wavephase velocity is maintained over a predetermined number of beamwavelengths over the tube overall length. The final or output section104 of the helix may have a pitch dimension somewhere between the valuesin sections 86 and 96 to provide for overall efficient beam-waveinteraction after the preconditioning of the electron beam modulation bythe dual velocity shift.

Several methods of achieving the phase velocity changes have beenheretofore noted. In any of the embodiments then, an electrical shiftcould be introduced in a wave-guiding structure having a uniform pitchthroughout by a DC voltage jump which would increase the average beamvelocity to a new level relative to the propagating wave velocity. Thismethod, however, has the disadvantage of requiring an additional powersupply and furthermore requires DC electrical isolation of the guidingstructure. Such a DC electrical isolation requirement gives rise to theneed for extremely careful circuit impedance matching. The illustrativestructural techniques, therefore, shown in FIGS. 4 and 5 from themechanical, as well as electrical standpoint, will generally be farsimpler. Of course, imaginative combinations of the wave phase velocityshift, as well as DC beam velocity voltage jump, may be advantageouslyexploited in the practice of the invention.

FIG. 6 illustrates still another facet of the invention is to provide avery elaborate profile of phase velocity characteristics to tailor abeam in many different ways to enhance efficiency. The particularteaching together with its fruition as depicted in FIG. 7 relates to theso-called ring and bar delay line 200 which is relatively dispersiveand, therefore, narrow band while the previously described helix-typeguiding structure is relatively nondispersive and ideal for octave orextremely wide bandwidths. Actually, the ring and bar arises from acontrawound helix configuration. The disclosed guiding structure will beutilized for highpower traveling wave devices capable of providing manythousands or even tens of thousands of watts of high-frequency energy.In some instances many ring and bar sections may be mounted in tandemwithin a common envelope with up-to-date heat removal structures. Thefirst portion or input section 108 of the overall profile diagramprovides for a uniform wave phase velocity and to this end the barsnumbered l43 inclusive of delay line 200 have a uniform spacing asindicated in the table FIG. 7. The structure referred to herein as barscomprises the solid portion 110 defined between the slotted sections 112and indicated by the symbol T. Conventionally, such delay lines aremachined from High-conductivity copper. It is a rather simple matter tomechanically alter the phase velocity configuration to the desiredprofile diagram by adjusting the overall length of each slotted sections112 to thereby increase or decrease the dimensions of the bar section10. The width of the slots will be maintained uniform throughout theillustrative embodiment. For the purpose of the present descriptionsection A and the table shown in FIG. 7 covers the first 63 bar membersand the secton designated B covers the remainder of the delay line frombars 64 to 123 inclusive. Further, to assist in the interpretation ofthis embodiment of the invention the bar width dimensions in inches havebeen shown on the right hand vertical coordinate of FIG. 6. These valuescan easily be related to the description of the phase velocity changesin the ensuing description.

The portion of the section A from bar 44 until bar 64 represents thefirst velocity shift which it will be noted, is gradually tapered asindicated by the line 114. In many instances the gradual tapering may bepreferable to a sharp drop in the velocity shift. Commencing from bar 44designated by the numeral 116 we note a gradual progressive decreasingof the overall bar dimension from a value of approximately 1.350 inchesto a value for bar number 63 denoted by numeral 118 of approximately0.246 inches. Bars 60-82 inclusive define the overall shift portion 120extending between sections A and B. At approximately the lowest point orin the vicinity of bars numbered 80 and 82 designated by the numerals122 and 124, we observe the minimal bar width dimensions. Atapproximately bar 84 designated by the numeral 124 we perceive thegradual restoration of the synchronizing condition to the new level ofphase velocity by gradually sloping line 126 and correspondinglyprogressively increasing bar width dimensions. In the remaining sectionof the ring and bar delay line we note another combination permissiblewithin the teachings of the invention by the provisions of a graduallylevel section 128 and then a decreasing tapered section 130 approachingthe output end. In this region we find the large signal region for theamplification of the propagated waves on the delay line structure. Theprofile diagram has been terminated at this point for the purpose of thedescription. In many applications it may be desirable to follow theforegoing velocity. shift sections with another substantially uniformsection at another phase velocity to provide for efficient synchronousinteraction between the propagated waves and the shifted electronbunches. The remaining bar dimensions shown in FIG. 7 consist of barmembers 132 and 134 indicates the members in the terminal portionofsection B of the illustrated line. To provide a detailed enumerationof the values calculated by the computerized-technique for exemplaryembodiment to handle extremely high-power microwave energy, attention isdirected to the complete tables shown in FIG. 7.

Referring next to FIG. 8 the discussion now turns to the application ofthe subject invention to the enchancement of efficiency in octavebandwidth tubes where premature saturation due to harmonic frequencyinterference has plagued traveling wave interaction devices. It has beenobserved in the computerized analysis and study of such devices that aconsiderable amount ofsecond harmonic frequency power actually exceedsthat of the fundamental frequency power at the low end of the band. Indevices having the observed second harmonic power exceedingly lowefficiencies in the overall tube performance were noted. In theillustration the curves indicate the normalized force versus phasevelocity for propagated waves near tube saturation to explain theinterference process of the second harmonic component with thefundamental frequency components. All the curves are shown to representone complete high-frequency RF energy cycle. Curve 136 is a plot of thefundamental space harmonic (F,). Curve 138 is a plot of the wave phasevelocity along the tube length dimension for the second harmonicfrequency components (F Curve 140, then, represents the total forcefield (F,+F versus wave phase velocity. Attention is directed to thefact that the second harmonic power level P jP,is calculated to be 10db. down from the fundamental and yet the relative force amplitude ofthe second harmonic stands at approximately 0.63 along the normalizedforce measurement coordinate. The beam bunch formation has been analyzedto have its charge density maximum occurring at approximately position Aor adjacent to the substantial midpoint of the fundamentalwavedecelerating electric field. As saturation is approacheddeceleration of the beam bunches occurs and they drift toward position Bunder the influence of the large combined high-frequency electricfields. This, it is believed, leads to premature tube saturation. Hence,it is this synchronous mechanism which has heretofore limited theefficiency attainment for, particularly, octave bandwidth traveling wavedevices where second harmonic frequencies are involved.

In accordance with the teachings of the invention, then, utilizingstructure heretofore described, as well as any other suitable structureknown to the artisan, the interference of the second space harmonicfield components on the amplification of the fundamental harmonicfrequencies may be substantially minimized by an appropriate shift atlow levels of beam modulation to move the beam-bunches forward in phaseto a position where the deceleration fields are minimal. Such a positionis designated by the position C within the accelerating field of thecurve 136. Since the second harmonic frequency components are lout ofphase at this point the fundamental frequency components still see thesynchronous condition for amplification of the fundamental frequencywaves now without the interference of the second harmonic fieldcomponent. As a result of the introduction of the velocity shift of, forexample well before the saturation level, measurable improvements inefficiency in octave bandwidth tubes by factors ofas high as 30to40percent have been noted by reason of the reduction of prematuresaturation previously induced by the second harmonic decelerationfields. Consequently, with this shift the second harmonic wave actuallyslips back in phase and favorably assists the beam-bunching processinduced by the fundamental wave.

In FIG. 9 three distinct possible combinations will be reviewed. Curve142 indicates a traveling wave device having a l5-percent phase velocityshift. The dotted line 144 depicts the phase of beam charge density fora device without the velocity shift mechanism. Finally, dashed line 146indicates the situation for the propagation ofa fundamental signal alonewithout any velocity shift. Clearly, the phase of the beam chargedensity shows a decided improvement in the region between 9-15 beamwavelengths for more efficient synchronous interaction.

The additional kinetic energy available for power conversion willprovide for an increase in efficiency as noted in the next illustration,FIG. 10. In this view the efficiency values are plotted along thevertical coordinate while the same distance dimensions in terms of beamwavelengths are indicated along the horizontal coordinate. The solidline 148 indicates a traveling wave device covering the second harmonic,as well as fundamental frequencies, with an approximate lS-percent phasevelocity shift in the wave-guiding structure. The dotted line 150 showsthe expected efficiency with the harmonic frequencies and no velocityshift which clearly results in efficiency degradation. Clearly then, itis evident that for a uniform wave-guiding circuit, particularly in theinstance of octave bandwidth tubes, the harmonic interference process issubstantial leading to premature saturation and very low efficiencies.

In FIG. 11 the illustration provides a comparison of harmonic powervariation as a function of distance along the tube length for comparisonof the results of embodiments incorporating the structure of theinvention. Curve 152 indicates the simulated power gain for thefundamental frequency only and no velocity shift. The dashed line 154appended to curve 152 indicates the 15 power gain with a velocity shiftof approximately ISpercent. Similarly, solid curve 156 is a simulationof the power gain of the second space hannonic frequency and the dashedline 158 indicates the drop and then recovery in gain of the secondharmonic power in a tube with the velocity shift. It is obvious from astudy of this illustration that the drop in gain in the second harmonicfrequency signal is substantially inconsequential in terms of theincrease in the power gain of the fundamental frequency signal. In thelarge signal region the reduced level of second harmonic power prolongssaturation with an accompanying increase in the fundamental signal powerin tubes with the velocity shift which produces improved phase focusing.The prior art efficiency degradation as a result of the excessive secondharmonic power content in octave bandwidth traveling wave devices has,therefore, been measurably improved through the introduction of thevelocity shift technique of the invention. At tube saturation thereduction in the second harmonic power content indicates thecontribution to the fundamental power gain.

A final alternative embodiment of the velocity shift technique of theinvention may be noted in FIG. 12 for incorporation in a device having asubstantially uniform wave-guiding circuit 160 with input and outputends 162 and 164, respectively. A suitable phase shifter indicatedgenerically by box 166 is coupled to the line in the region closelyadjacent to the input end or the region of low level beam modulation tointroduce the desired shift of the phase velocity characteristics ashereinbefore outlined. In this manner the phase of the waves beingpropagated may be delayed by any value up to 90to provide for theadvancement of the electron bunches to the minimal region of thedecelerating electric fields of the propagating waves.

The realization that the tailoring of the beam-wave velocitycharacteristics in the initial stages of beam modulation mayconsiderably affect or enhance efficiency should be an impetus in thefurther utilization of both narrow, as well as octave bandwidthtraveling wave interaction devices, for communications, as well as radarsystem applications. Both the second harmonic frequency interferenceprocess, as well as narrow band fundamental frequency signalamplification and/or generation, have been discussed in the foregoingdescription. There is a wide range of combinations which may be evolvedin the practice of the invention to provide tube output characteristicsheretofore believed unattainable utilizing prior art utilizing prior artstructures. In view, therefore, of the many variations modifications andalterations which will be apparent to those skilled in the art relatingto the disclosed invention, the foregoing description is intended as onefor illustrative purposes only. All such variations, therefore, areintended to be encompassed by the broad interpretation of the scope andbreadth of the invention as set forth and defined in the appendedclaims.

What is claimed is:

1. A traveling wave electron interaction device comprising:

a wave-guiding circuit means for propagating electromagnetic waveenergy;

means for generating and directing a beam of electrons along a pathadjacent to said wave-guiding circuit means to interact in an energyexchanging relationship with the propagated waves;

and means for varying the electron beam-wave interaction relationship byreducing the circuit phase velocity ratio (Vp/C) where C is the velocityoflight at substantially low levels of beam modulation sufficient toprovide for a shift in electron bunching within the deceleratingelectric fields of said propagated waves and increase the net overallenergy transfer between said electrons and said waves.

2. A traveling wave electron interaction device comprising.

wave-guiding circuit means for propagating electromagnetic wave energy;

means for generating and directing a beam of electrons along a pathadjacent to said wave-guiding circuit means to interact in an energyexchanging relationship with the propagated waves;

and means for introducing a discontinuity in the phase velocitycharacteristics of said guiding circuit means at an intermediate regionalong said interaction path to reduce said phase velocity;

said region being oriented at substantially low levels of beammodulation sufficient to provide for optimal bunching of electronswithin the decelerating electric fields of said propagated waves toincrease the net overall energy transfer between said electrons and saidwaves. 3. A traveling wave electron interaction device comprising:wave-guiding circuit means having an input and output terminal forpropagating electromagnetic wave energy; means for generating anddirecting a beam of electrons along a path adjacent to said wave-guidingcircuit means to interact in an energy exchanging relationship with thepropagated waves; and means for varying the electron beam velocitycharacteristics by reducing the circuit phase velocity ratio (Vp/C)where Cis the velocity of light at substantially low levels of beammodulation sufficient to provide for advancement in phase of themodulating electron bunches relative to the decelerating electric fieldsof said propagated waves in a direction toward the output terminal andincrease the net overall energy transfer. 4. A traveling wave electroninteraction device comprising: a wave-guiding circuit for propagatingelectromagnetic waves; means for regenerating and directing a beam ofelectrons along a path adjacent to said circuit to interact in an energyexchanging relationship with said waves;

and means for varying the electron beam-wave interaction relationship byreducing the circuit phase velocity ratio (Vp/C) where Cis the velocityoflight at substantially low levels of beam modulation sufficient toprovide for an advance in phase of electron bunching relative to thewaves on said circuit of between 45-90 within the decelerating electricfields of said waves with a resultant increase in net overall energytransfer. 5. A traveling wave electron interaction device comprising: Awave-guiding circuit for propagating electromagnetic waves;

means for generating and directing a beam of electrons along a pathadjacent to said circuit to interact in an energy-exchangingrelationship with said waves; and means for varying the electronbeam-wave interaction characteristics by reducing the circuit phasevelocity (vp/C) where Cis the velocityof light sufficient to provide foran advance in phase of the modulating electron bunches relative to thedecelerating electric fields of said waves at a point l0to 20 db. belowthe saturation level of the device. 6. A traveling wave electroninteraction device comprising a wave-guiding circuit having an input andoutput terminal for propagating electromagnetic waves; means forgenerating and directing a beam of electrons along a path adjacent tosaid circuit to interact in an energy exchanging relationship with saidwaves; and means for varying the electron beam-wave interactioncharacteristics by reducing the circuit phase velocity (Vp/C where C isthe velocity of light to provide for an advance in phase of themodulating electron bunches relative to the decelerating electric fieldsof said waves in a region along the length of the device where the valueof the electromagnetic circuit power level is in the order of 1 percentof power at the output terminal. 7. A traveling wave electroninteraction device comprising: a wave-guiding circuit structure forpropagating electromagnetic waves; means for generating and directing abeam of electrons along path adjacent to said structure to interact inan energy-exchanging relationship with said waves; and means for varyingthe electron beam-wave interaction characteristics by reducing thecircuit phase velocity ratio (Vp/C) where C is the velocity oflight inthe region of substantially low levels of beam modulation in conformancewith a mathematically programmed profile pattern to introduce adesynchronizing characteristic in the relationship of the phase of saidelectron and propagated wave velocities and shift the characteristics(Vp/C) where C is the velocity of light to yield a substantiallynonsynchronous relationship over a portion of said interaction path inthe region of substantially low levels of beam modulation and shift thevelocity of electron beam bunches within the decelerating electricfields of said waves;

and means for establishing a synchronous interaction relationship with apredetermined ratio of electron beam to wave velocity disposedsequentially to said velocity shift region.

Patent No.

Inventor (8) Column Column Column Column Column Column Column ColumnColumn Column Column Column Column UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Dated October 19, l97l Norman J. Dionne It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

3, line 18, change "l-l" to .l l

4, line 65, change "ED3" to ED-3 4, line 68, change "Standford" toStanford 5, line 51, equation (4) change (Z/u t)" to 5, line 65,equation (5a) change 1+C b 2 to "2 z 5, line 71, equation (5b) change 2Tto Z? 6, line 44, delete "n/" and insert to the 6, line 50, change "nC bto nC b 7, line 30, change "Ovalue" to 0 value 7, line 39, change"02.0.3" to 0.2-0.3

8, line 1, change "01." to 1.0

9, line 2, change "(VpC)" to (Vp/C) 10, line 48, after "invention"delete "is" ORM 1 0-1050 (10-69) USCOMM'DC GOEITG-PGQ n U 5 GOVERNMENTPRINTING OFFICE 199 OJ66 33A Page Two UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3, 614, 517 Dated o i 1 9 1 91]Inventor() NOIman J. Dionne It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 10, line 70, change "High-conductivity" to high-conductivityColumn 10, line 74, change "10." to 110.

Column 11, line 44, delete "15" and insert the Column 12, line 18,delete "accelerating" and insert decelerating Column 12, line 65, delete"l5" and insert additional Column 14, line 42, claim 5, change "(vp/C)to (Vp/C) Signed and sealed this nth day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTI'SCHALK Attesting Officer Commissionerof Patents USCOMM'DC 60376-F'69 DRM PO 105CI (10-69) a u s covmumzmmurmur, ornc: mu 035$-134

1. A traveling wave electron interaction device comprising: awave-guiding circuit means for propagating electromagnetic wave energy;means for generating and directing a beam of electrons along a pathadjacent to said wave-guiding circuit means to interact in an energyexchanging relationship with the propagated waves; and means for varyingthe electron beam-wave interaction relationship by reducing the circuitphase velocity ratio (Vp/C) where C is the velocity of light atsubstantially low levels of beam modulation sufficient to provide for ashift in electron bunching within the decelerating electric fields ofsaid propagated waves and increase the net overall energy transferbetween said electrons and said waves.
 2. A traveling wave electroninteraction device comprising. wave-guiding circuit means forpropagating electromagnetic wave energy; means for generating anddirecting a beam of electrons along a path adjacent to said wave-guidingcircuit means to interact in an energy exchanging relationship with thepropagated waves; and means for introducing a discontinuity in the phasevelocity characteristics of said guiding circuit means at anintermediate region along said interaction path to reduce said phasevelocity; said region being oriented at substantially low levels of beammodulation sufficient to provide for optimal bunching of electronswithin the decelerating electric fields of said propagated waves toincrease the net overall energy transfer between said electrons and saidwaves.
 3. A traveling wave electron interaction device comprising:wave-guiding circuit means having an input and output terminal forpropagating electromagnetic wave energy; means for generating anddirecting a beam of electrons along a path adjacent to said wave-guidingcircuit means to interact in an energy exchanging relationship with thepropagated waves; and means for varying the electron beam velocitycharacteristics by reducing the circuit phase velocity ratio (Vp/C)where Cis the velocity of light at substantially low levels of beammodulation sufficient to provide for advancement in phase of themodulating electron bunches relative to the decelerating electric fieldsof said propagated waves in a direction toward the output terminal andincrease the net overall energy transfer.
 4. A traveling wave electroninteraction device comprising: a wave-guiding circuit for propagatingelectromagnetic waves; means for regenerating and directing a beam ofelectrons along a path adjacent to said circuit to interact in an energyexchanging relationship with said waves; and means for varying theelectron beam-wave interaction relationship by reducing the circuitphase velocity ratio (Vp/C) where C is the velocity of light atsubstantially low levels of beam modulation sufficient to provide for anadvance in phase of electron bunching relative to the waves on saidcircuit of between 45*-90* within the decelerating electric fields ofsaid waves with a resultant increase in net overall energy transfer. 5.A traveling wave electron interaction device comprising: A wave-guidingcircuit for propagating electromagnetic waves; means for generating anddirecting a beam of electrons along a path adjacent to said circuit tointeract in an energy-exchanging relationship with said waves; and meansfor varying the electron beam-wave interaction characteristics byreducing the circuit phase velocity (vp/C) where Cis the velocity oflight sufficient to provide for an advance in phase of the modulatingelectron bunches relative to the decelerating electric fields of saidwaves at a point 10to 20 db. below the saturation level of the device.6. A traveling wave electron interaction device comprising awave-guiding circuit having an input and output terminal for propagatingelectromagnetic waves; means for generating and directing a beam ofelectrons along a path adjacent to said circuit to interact in an energyexchanging relationship with said waves; and means for varying theelectron beam-wave interaction characteristics by reducing the circuitphase velocity (Vp/C ) where C is the velocity of light to provide foran advance in phase of the modulating electron bunches relative to thedecelerating electric fields of said waves in a region along the lengthof the device where the value of the electromagnetic circuit power levelis in the order of 1 percent of power at the output terminal.
 7. Atraveling wave electron interaction device comprising: a wave-guidingcircuit structure for propagating electromagnetic waves; means forgenerating and directing a beam of electrons along path adjacent to saidstructure to interact in an energy-exchanging relationship with saidwaves; and means for varying the electron beam-wave interactioncharacteristics by reducing the circuit phase velocity ratio (Vp/C)where C is the velocity of light in the region of substantially lowlevels of beam modulation in conformance with a mathematicallyprogrammed profile pattern to introduce a desynchronizing characteristicin the relationship of the phase of said electron and propagated wavevelocities and shift the electron beam bunches within the deceleratingelectric fields of said waves to a more favorable energy exchangingposition with a resultant increase in net overall energy transfer.
 8. Atraveling wave electron interaction device comprising: a periodic slowwave circuit structure for propagating electromagnetic waves; means forgenerating and directing a beam of electrons along a path adjacent tosaid structure to interact in an energy exchanging relationship withsaid waves; means for reducing the ratio of electron beam-wave velocitycharacteristics (Vp/C) where C is the velocity of light to yield asubstantially nonsynchronous relationship over a portion of saidinteraction path in the region of substantially low levels of beammodulation and shift the velocity of electron beam bunches within thedecelerating electric fields of said waves; and means for establishing asynchronous interaction relationship with a predetermined ratio ofelectron beam to wave velocity disposed sequentially to said velocityshift region.